The present invention relates generally to a screw locking assembly including a hollow split stud or split bolt and a screw set-pin that is tightened into the hollow split bolt to lock it tightly into a hole or threaded hole in a medial body. More particularly, the present invention relates to improvements that greatly increase the mechanical advantage between torque applied to the pin setscrew and expansion of a split distal end portion of the bolt and to preventing loosening of the pin setscrew with respect to the split bolt and to preventing loosening of the split bolt with respect to the bolt-receiving hole without galling and causing injury to the threads of either the bolt bore or the pin setscrew as in the prior art.
The closest prior art is believed to include U.S. Pat. No. 322,657 entitled “Screw Bolt Lock” issued to Tolman on Jul. 21, 1885, U.S. Pat. No. 2,463,859 entitled “Threaded Locking Device” issued Jul. 25, 1945 to Engstrom, and U.S. Pat. No. 2,479,075 entitled “Screw Locking Means” issued to Martin on Nov. 24, 1944.
U.S. Pat. No. 322,657 discloses a screw bolt lock including a screw bolt A with a threaded central aperture C having a tapered section E and accommodating a screw or center pin F that spreads a slitted end section D of the bolt apart to lock the bolt into a threaded hole. As shown in FIG. 1 of U.S. Pat. No. 322,657, the center pin F is threaded up to the tapered section E of the bolt bore. The bolt bore is threaded to the point at which the distal end of the bore becomes tapered.
Similarly, U.S. Pat. No. 2,479,075 discloses a device in which a screw 11 having a bore 14 with slits 13 accepts a threaded plug 21 having a conical end taper 19 conforming to a tapered end section 17 of the bore. The tightening of the threaded plug is described as causing the conical end taper of the threaded plug to engage the tapered bore section 17, thereby expanding the slitted end of the screw 11 and locking it into a threaded hole of a body. U.S. Pat. No. 2,463,859 discloses another similar device in which a bolt has a partially threaded bore 4 that extends from the head of the bolt to a distal end portion thereof. Slits 8 are formed in the distal end portion of the bolt. A threaded expander stud 9 is threaded into bolt bore 4 to the end of the threaded portion. Further tightening of the stud causes it to engage a reduced diameter distal portion of the bore 4, causing expansion of the slitted distal end of the bolt, thereby locking the slitted distal end into a threaded hole.
The devices disclosed in the above described references have the shortcoming that the pin setscrews disclosed in the above references “bottom out” or “heel” on the lead-in threads of the bolt bore before the tapered distal end section of the pin setscrew reaches the tapered section of the bolt bore. The tapered distal end of the pin setscrew never comes in contact with the tapered section of the inner bore of the bolt because of the commonly known lead-in threads, required on all tapped blind holes, which bind the pin in the lead-in threads before it can reach the tapered section of the inner bore of the bolt. Tightening of the center pin, referred to herein as the “pin setscrew”, in order to advance its distal threaded section sufficiently further into the unthreaded section of the bolt bore to spread the distal end of the bolt would cause the threads of the pin setscrew to gall on the threads of the bolt and cause strain and injury to the threads of both the pin setscrew and the bolt such that neither would be reusable, as recognized in the Tolman patent. (The term “galling” refers to a severe form of adhesive way or that occurs during sliding contact of one surface relative to another, wherein clumps of one part may break away from one surface and stick to the other surface.) Such galling would necessitate that an extremely large amount of torque be applied to the pin setscrew to advance it into the reduced-diameter portion of the bolt bore. Also, there would be inadequate mechanical advantage of torque applied between the bolt end of the pin setscrew to advance the pin setscrew so as to develop sufficient outward force on the split distal end sections of the bolt to expand them and adequately lock the bolt into the bolt-receiving hole. It would not be practical for the user to apply enough force to the pin setscrew to spread the distal split end of the bolt enough to cause an adequate locking effect, and the force would not be equally applied to all fingers to spread the bolt because of the diminishing root depth of the lead in threads of the bolt bore screw section as the pin setscrew is turned. Furthermore, the prior art does not provide any way of locking the pin setscrew to the bolt into when it is screwed into the bolt.
Despite the efforts in the prior art, there has been a very long and unfulfilled need for a practical, highly reliable self-locking bolt. For more than 200 years there has been a need for a locking fastener that is simple to use without use of parts that need to be assembled while installing and locking the fastener. An example of an application in which there has been a very long felt need for a reliable self-locking bolt is in the field of high-performance internal combustion engines, wherein exhaust manifold bolts frequently become loosened due to vibration and thermal cycling. No really reliable solution to this problem has ever been provided. There also are numerous other examples in which there has been a long felt need for a reliable self-locking bolt, including engine oil pump mounting applications, industrial press brake tool attachment applications, mining wheel and hub attachment applications, railroad track attachment applications, and many more.
There also is an unmet need for a simple true locking fastener that surpasses the IFI-124 and MIL-DTL-18240F specifications wherein the bolt and pin assembly securely locks, does not unlock under vibration or heat stress, and is not torque-dependent.